1. Field of the Invention
This invention relates in general to a branching method for splitting off individual buffered fibers from a multifiber fiberoptic cable and more particularly to a branching method utilizing an injection mold wherein the buffered fibers are not subject to stress during or after the injection molding process and wherein the integrity of the strength member of the cable system is maintained throughout its length and, in particular, throughout the branching point.
2. Description of the Prior Art
Fiberoptic cables are quickly displacing copper wiring as the medium of choice in local area network systems. The fiber environment, however, raises certain unique problems resulting from the delicate nature of fibers. For example, fiberoptic systems are extremely susceptible to signal loss or distortion, and even permanent damage to the fiber, when excessive bending of the fiber occurs or when forces such as pulling or crushing are exerted on the fiber.
These problems have been addressed by the placement of fibers within a cable comprised of an outer jacket, which in turn surrounds a strength member comprised of aramid fibers, such as kevlar, which in turn surrounds one or more buffered fibers. This cable system allows stress from pulling and crushing to be absorbed by the outer jacket and strength member. In addition, these components provide a certain degree of rigidity to the cable, thereby protecting against extreme bending. Even with these features, however, fiberoptic cables must still be handled with care.
Multi-fiber fiberoptic cables, i.e., fiberoptic cables with two or more buffered fibers, are generally used in network systems. As a result, it often becomes necessary to branch off an individual buffered fiber from the multi-fiber fiberoptic cable. This branching off, however, may result in a weak point in the system. In particular, the branching point may be highly susceptible to bending or other stresses. Furthermore, the integrity of the strength member may be compromised or even eliminated at the branching point.
These problems are well known and a number of prior art methods and devices have been used to attempt to resolve these problems. Each of these methods or devices, however, has disadvantages and fails to protect the integrity of the strength member and/or the fiber itself.
For example, one method that is used is to branch off the individual fibers and provide each individual fiber with its own covering of kevlar and a jacket. Thereafter, the kevlar coverings of the multi-fiber cable and the individual fibers are tied together and then this junction point is bound by heat shrink tubing. This method fails to maintain the continuous stress relief of the kevlar and, more importantly, the junction point is susceptible to bending or shifting, which can easily damage the fibers.
Another prior art device secures the opposing kevlar sections with ferrules which are in turn secured within a hollow plastic mold. This device depends on the strength of the plastic mold to maintain the continuous stress relief of the kevlar, is costly to produce and is labor intensive. More importantly, between the opposing ferrules there is a portion of exposed fiber. While this exposed fiber is enclosed within the hollow plastic mold, it is susceptible to being completely ruined if the hollow mold is crushed.
Another prior art device is disclosed in U.S. Pat. No. 4,976,508 wherein the use of a housing and potted resin is suggested. This device has numerous drawbacks, including optical loss resulting from the lack of stability of the fiber in the hollow housing or the force exerted on the fiber if resin is poured into the hollow housing.
These problems are recognized in a related patent, U.S. Pat. No. 4,989,945. Even the attempt to rectify these problems, as disclosed in this second patent, also falls short of the mark. In particular, among its disadvantages, the device disclosed in this second patent still has a portion of exposed fiber that is subject to stress when resin is introduced into the device.
Those prior art devices that disclose the use of resin as a means for securing the strength member disclose the use of a potted resin. A much quicker and cleaner molding process is injection molding. The use of injection molding with respect to fiberoptic branching applications has been limited, however, inasmuch as the injection molding process may exert a substantial amount of stress on those elements within the interior of the mold.